Energy Efficiency Analysis of Multi‐Fuel Cell Stack System for Forklifts Based on Three Energy Management Strategies

ABSTRACT

Proton exchange membrane fuel cells (PEMFC) is considered one of the most promising sources of electric energy, playing a particularly important role in small and medium‐sized specialty vehicles such as forklifts. However, in practice, for low‐power electric vehicles like forklifts, there is a lack of real‐world operating conditions to support the study of top‐ and bottom‐level energy management strategies for multiple stacks. Therefore, this paper conducted on‐site testing of the electric forklift, collected the output power during operation, and designed comprehensive actual operation test conditions. The energy management strategy adopts a hierarchical approach. Three top‐level energy management strategies are proposed for the dual stacks and batteries: charging strategy, fuzzy division strategy, and power interval following strategy. The bottom‐level energy management strategy between the two stacks aims for optimal efficiency. Based on the actual continuous operating profile of the forklifts, the three strategies are analyzed, along with the system's hydrogen consumption, battery state of charge (SOC) variations, and dynamic fuel cell load variations under series and parallel configurations. The results show that while the power interval following strategy can maintain the SOC within a stable range, it results in a high fuel cell load output frequency. The charging and fuzzy partitioning strategies provide better protection for fuel cell health. Furthermore, the system's equivalent hydrogen consumption is low under high initial SOC and the series configuration. The fuzzy division strategy can reduce hydrogen consumption by up to 9.66%. Mathematical analysis of the extended polarization curve diagram proves that two battery stacks with poor consistency and increasing pressure difference with increasing current are more efficient when connected in parallel in the concave section of their polarization curves.